A Just Released Windows Update Fixes Kerberos Security Hole

Microsoft has released an unscheduled update to patch a critical security hole that is being actively exploited to hack Windows-based servers. It is important that you update your servers now. Contact 123 Support if you need an assessment of this risk today.


“A flaw in the Windows implementation of the Kerberos authentication protocol allows attackers with credentials for low-level accounts to remotely hijack extremely sensitive Windows domain controllers that allocate privileges on large corporate or government networks. The privilege elevation bug is already being exploited in highly targeted attacks and gives hackers extraordinary control over vulnerable networks.”

“The only way a domain compromise can be remediated with a high level of certainty is a complete rebuild of the domain,” Microsoft engineer Joe Bialek wrote in a blog post accompanying Thursday’s patch. “An attacker with administrative privilege on a domain controller can make a nearly unbounded number of changes to the system that can allow the attacker to persist their access long after the update has been installed. Therefore it is critical to install the update immediately.”

While all supported versions of Windows contain the bug fixed Tuesday, server versions from 2008 R2 and earlier are the most vulnerable. The exploits observed so far work against Windows Server 2008 R2 and previous server versions. Domain controllers running on Windows Server 2012 and higher aren’t susceptible to those attacks, but they are vulnerable to a related technique that is harder to carry out. Windows systems that don’t run domain controllers are theoretically vulnerable. Bialek said all Windows users should install the patch as soon as possible, but the priority should be assigned in the following order: (1) domain controllers running 2008 R2 and below, (2) domain controllers running server 2012 and higher, and (3) all other systems running any supporter version of Windows.